CONTRACTION STRESS TEST

The contraction stress test (CST) assesses the ability of the fetus to tolerate
transitory decreases in intervillous blood flow that occur with uterine
contractions. It uses both external FHR and contraction monitoring devices and
is based on the presence or absence of late decelerations. These are gradual
decreases in FHR below the baseline with onset to nadir of ≥30 s. The
deceleration onset and end is delayed in relation to contractions. If 3
contractions in 10 min are not spontaneously present, they may be induced with
IV oxytocin infusion or nipple stimulation. This test is rarely performed
because of the cost and personnel time required. The most common indication is
a BPP of 4 or 6.

Negative    CST requires    absence of  any late    decelerations   with    contractions.

This    is  reassuring  and highly  reassuring  for fetal   well-being. Management  is

to  repeat  the CST weekly. Fetal   death   rate    is  only    1   per 1,000   in  the next

week.

Positive    CST is  worrisome.  This    requires    the presence    of  late    decelerations

associated  with    at  least   50% of  contractions.   50% of  positive    CSTs    are false-

positive    (meaning    the fetus   is  not hypoxemic). They    are associated  with    good

FHR variability.    The 50% of  true-positives  are associated  with    poor    or  absent

variability.    Management  is  prompt  delivery.

Contraindications   include situations  when    contractions    would   be  hazardous   to

the mother  or  fetus,  e.g.,   previous    classical   uterine incision,   previous

myomectomy, placenta    previa, incompetent cervix, preterm membrane

rupture,    and preterm labor.